1. Field of the Invention
The present invention relates to a rechargeable battery that has improved current collecting efficiency.
2. Background of the Invention
Unlike a nonrechargeable battery that may not be recharged, a rechargeable battery may be charged and discharged repeatedly. A lithium rechargeable battery may be packaged into a pack shape to be used as a power source for various portable electronic devices such as cellular phones, laptop computers, and camcorders.
Recently, rechargeable batteries with high power storage capacity have been developed for use as power sources for driving motors such as those in hybrid automobiles.
These rechargeable batteries may be fabricated into various shapes such as cylindrical and rectangular box shapes in which an electrode assembly comprising positive electrode sheets, negative electrode sheets, and a separator that is interposed between the electrode sheets is wound (as a jelly roll) and inserted into a case. The case is mounted with a cap assembly that is formed with outer terminals to provide a battery.
An electrode assembly includes leads at the positive electrode and the negative electrode to collect current that is generated at the positive electrode and the negative electrode during the cell operation. The leads are connected to external terminals to which the current is supplied.
This structure may provide sufficient current collection efficiency in a small-sized battery that has a low power storage capacity. However, a structure that collects current using leads is inefficient in a large-size battery that requires high power output. For example, the sizes of the positive electrode and the negative electrode increase in proportion to the size of the battery as do the resistances of a larger-sized positive electrode and negative electrode. In addition, the above-described structure has difficulty in evenly outputting the current that is generated in every part of the electrode assembly when it is used in the large-sized battery.
To resolve these problems, Japanese Patent Laid-Open No. Hei 06-267528 discloses a rechargeable battery that is manufactured by forming lead adhesion regions that are not coated with an active material at one end of current collectors of the band-type positive and negative electrodes. The lead adhesion regions protrude higher than the separator when an electrode assembly is formed by winding the positive electrode, the negative electrode and the separator. A plurality of positive electrode leads and negative electrode leads are coupled to the lead adhesion regions.
Since a conventional rechargeable battery may attach a plurality of lease in the lead adhesion regions, it can have an increased current collecting efficiency by reducing internal resistance of the battery and collecting current from the positive electrode and the negative electrode. This rechargeable battery is difficult to manufacture because a plurality of leads are fixed in the lead adhesion region. Also, since an active material is not present inside the cell, the capacity of the portion that does not participate in the reaction, that is, the portion occupied by the lead adhesion regions and the leads, becomes large, which makes it hard to form a large-size high-power battery.
Japanese Patent Laid-Open No. 2000-40501 discloses a structure where terminals are connected to projecting ends of an electrode assembly that are not coated with an active material. The technology, however, cannot maximize the current collecting efficiency because the contact area of the unit that substantially connects the projecting ends to the terminals electrically is restrictive.